|Wilkesia gymnoxiphium growing near Waimea Canyon|
Wilkesia gymnoxiphium (Hawaiian iliau), is a species of flowering plant in the sunflower family, Asteraceae, that is endemic to the island of Kauaʻi in Hawaiʻi. Wilkesia is one of three genera, with Argyroxiphium (silverswords and greenswords) and Dubautia (a larger group with many varied species) that are believed to be descendant from a single species related to the North American tarweed. The members of these three genera constitute what is called the silversword alliance, a group whose exceedingly close genetic heritage is not reflected in their exceptionally diverse morphologies.
W. gymnoxiphium is a monocarpic rosette shrub, with rosettes elevated on woody stems as much as 5 m (16 ft) tall. Distinctive features include a usually unbranched, monocarpic axis, leaves in whorls of 9-15 that join to form a basal sheath around the stem, and peduncles that are commonly branched. Fountains of yellow, daisy-like flowers form mostly May to July. When unbranched the plant dies after flowering, but if it branches into multiple heads (as may happen if the top is broken off), each head will flower and die separately.
This species occurs only on Kauaʻi, on dry ridges or dry to mesic forests. The most common location is along the slopes of Waimea Canyon. It grows at elevations of 425–1,100 m (1,394–3,609 ft) in areas that receive 800–2,000 mm (31–79 in) of annual precipitation.
Heavily grazed by feral goats in the canyon, they are most often seen on inaccessible slopes. However, a dense population can be seen in a fenced enclosure just off the road heading to Kōkeʻe State Park.
- "Wilkesia gymnoxiphium A. Gray". Germplasm Resources Information Network. United States Department of Agriculture. 2003-04-03. Retrieved 2009-10-31.
- Carlquist, Sherwin (1980). Hawaii, a natural history: geology, climate, native flora and fauna above the shoreline. Lawai: Pacific Tropical Botanical Garden. pp. 250–266.
- "Adaptive Radiation and Hybridization in the Hawaiian Silversword Alliance". University of Hawaii Botany Department. Retrieved December 8, 2009.
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